This invention relates generally to a fuel burner pumping system having provision for automatically purging air from the system. More particularly, the invention is especially adapted for use in a pumping system which uses fuel in the form of heavily contaminated waste oil of comparatively high viscosity.
The pumping system of the invention is a so-called two-pipe system, meaning that one pipe (an intake pipe) leads from a fuel supply tank to the pump of the pumping system to deliver fuel from the tank to the pump while a second pipe serves as a return pipe to the tank. In prior two-pipe systems, excess fuel oil which is not required by the burner passes through a seal chamber in the pump and is returned to the tank via the second pipe. Any air which is in the system at start-up passes from the seal chamber to the tank with the excess oil and is automatically bled from the system at the tank. A seal is located in the seal chamber and establishes a seal around the shaft of the pump.
Two-pipe systems of the type described above present special problems when the fuel being pumped is waste oil. Because such oil is of high viscosity, it is necessary to maintain a low velocity flow in the intake line between the tank and the pump in order to prevent cavitation at the pump. When a large flow of excess oil is returned to the tank by way of the second pipe, the flow from the tank back to the pump also is large and this creates a relatively high velocity in the intake line. If relatively large quantities of heavily contaminated waste oil pass through the seal chamber of the pump, the seal of the pump may experience only a limited life and the shaft of the pump may experience excessive wear.